1. Field of the Invention
The present invention relates to the separation of the rare earth values contained in minerals or concentrates rich in rare earth fluocarbonates and, in particular, bastnaesite. More especially, this invention relates to the improved separation of neodymium values from bastnaesite ores, possibly in combination with praseodymium and other rare earths contained therein.
By the term "rare earths" as utilized herein are intended the rare earth elements of the Periodic Table having atomic numbers of from 57 to 71, as well as yttrium which has an atomic number of 39.
In the description which follows, by the term "ceric rare earths" are intended the lightest rare earth elements by atomic numbers, beginning with lanthanum and extending to neodymium, and by the term "yttric rare earths" are intended the heaviest rare earths according to atomic numbers, beginning with samarium and extending to lutecium, and including yttrium. Also, by the term "trivalent rare earths" are intended the rare earth elements having the atomic numbers of 39, 57, 59 to 71.
The term "didymium" is a common designation for a mixture of neodymium and praseodymium, regardless of the proportions thereof.
Further, by the term "bastnaesite" is broadly intended a rare earth mineral comprising rare earth fluocarbonates, either with or without another component, in particular a mineral gangue, together with concentrates of these minerals.
2. Description of the Prior Art
The development of magnets based on the rare earths alloyed with iron, and more particularly those based on neodymium and praseodymium, mandate the availability of technically and economically efficient processes for the separation of such values.
Those processes currently used for the purification of rare earths from minerals are directed either at the recovery of all of the rare earths separated, which is difficult and expensive, or at a recovery of a fraction rich in the higher priced rare earths, in particular europium, the yttric rare earths and yttrium itself.
Numerous processes have been described and are used industrially to realize the aforementioned objectives, beginning with the conventional raw materials for the production of the rare earths, e.g., onazite, bastnaesite or xenotime.
Those processes heretofore proposed for the complete recovery of the rare earths typically employ decomposition with sodium hydroxide, followed by redissolution of the resulting hydroxides with hydrochloric or nitric acid. From solutions of the rare earth chlorides or nitrates, the rare earths values are separated from each other by successive liquid/liquid extractions.
In the case of bastnaesite, as described in Deco Trefoil, p.9, (November-December, 1967), a precalcination of the mineral may be employed, which makes it possible to solubilize only a part of the cerium with the mixture of the other rare earths during the subsequent recovery operation using hydrochloric acid. Beginning with the solution of the rare earth chlorides, a solvent separation of europium and the yttric fraction of rare earths is carried out.
As heretofore mentioned, although these processes enable the recovery of neodymium and praseodymium, they are not capable of effecting such purpose under satisfactory conditions relative to each intended application.